NullPointerException异常:姓名== NULL [英] NullPointerException: name == null
问题描述
我正在开发一个使用碎片Android应用程序。我得到这个错误。
I'm developing an Android application that uses Fragments. I got this error.
Caused by: java.lang.NullPointerException: name == null
这是什么名== NULL
是什么意思?下面是完整的日志
What does name == null
mean? Here's the full log
08-04 15:02:22.422: E/AndroidRuntime(2499): FATAL EXCEPTION: main
08-04 15:02:22.422: E/AndroidRuntime(2499): java.lang.RuntimeException: Unable to start activity ComponentInfo{fi.peltoset.mikko.home/fi.peltoset.mikko.home.Koti}: android.view.InflateException: Binary XML file line #17: Error inflating class fragment
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.os.Handler.dispatchMessage(Handler.java:99)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.os.Looper.loop(Looper.java:137)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.main(ActivityThread.java:4745)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.reflect.Method.invokeNative(Native Method)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.reflect.Method.invoke(Method.java:511)
08-04 15:02:22.422: E/AndroidRuntime(2499): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-04 15:02:22.422: E/AndroidRuntime(2499): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-04 15:02:22.422: E/AndroidRuntime(2499): at dalvik.system.NativeStart.main(Native Method)
08-04 15:02:22.422: E/AndroidRuntime(2499): Caused by: android.view.InflateException: Binary XML file line #17: Error inflating class fragment
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
08-04 15:02:22.422: E/AndroidRuntime(2499): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:256)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Activity.setContentView(Activity.java:1867)
08-04 15:02:22.422: E/AndroidRuntime(2499): at fi.peltoset.mikko.home.Koti.onCreate(Koti.java:13)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Activity.performCreate(Activity.java:5008)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
08-04 15:02:22.422: E/AndroidRuntime(2499): ... 11 more
08-04 15:02:22.422: E/AndroidRuntime(2499): Caused by: java.lang.NullPointerException: name == null
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.VMClassLoader.findLoadedClass(Native Method)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:354)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.ClassLoader.loadClass(ClassLoader.java:491)
08-04 15:02:22.422: E/AndroidRuntime(2499): at java.lang.ClassLoader.loadClass(ClassLoader.java:461)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Fragment.instantiate(Fragment.java:574)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Fragment.instantiate(Fragment.java:552)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.app.Activity.onCreateView(Activity.java:4656)
08-04 15:02:22.422: E/AndroidRuntime(2499): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:680)
08-04 15:02:22.422: E/AndroidRuntime(2499): ... 21 more
这是一类被称为导航
。它扩展了 android.app.Fragment
。
This is in a class called Navigation
. It extends android.app.Fragment
.
在它的 onCreateView
方法,我膨胀的布局,并将其返回。在 onActivityCreated
方法,我检查,如果布局有两个窗格(我有不同的布局,为不同的设备),并基于该我加onClickListeners这些。
In it's onCreateView
method I inflate the layout and return it. In the onActivityCreated
method I check if the layout has two panes (I have different layouts for different devices) and based on that I add onClickListeners to these.
我的code看起来是这样的。
My code looks like this.
public class Navigation extends Fragment {
private OnItemSelectedListener listener;
private boolean dualPane = false;
public interface OnItemSelectedListener {
public void onMenuItemSelected(int fragmentId);
}
public void onAttach(Activity activity) {
super.onAttach(activity);
if(activity instanceof OnItemSelectedListener) {
this.listener = (OnItemSelectedListener) activity;
} else {
...
}
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_navigation, container, false);
return view;
}
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
View contentPane = getActivity().findViewById(R.id.contentFragment);
dualPane = contentPane != null && contentPane.getVisibility() == View.VISIBLE;
if(dualPane) {
final ListView menu = (ListView) getActivity().findViewById(R.id.valikko);
menu.setChoiceMode(ListView.CHOICE_MODE_SINGLE);
String[] texts = new String[] {
...
};
ArrayList<MenuItem> items = new ArrayList<MenuItem>();
items.add(new MenuItem("Home", R.drawable.koti2));
...
ImageArrayAdapter adapter = new ImageArrayAdapter(getActivity(), items, texts);
menu.setAdapter(adapter);
menu.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String item = ((TextView) view.findViewById(R.id.label)).getText().toString();
listener.onMenuItemSelected(0); // TODO ...
}
});
} else {
ImageView btnYleiskatsaus = (ImageView) getActivity().findViewById(R.id.btnYleiskatsaus);
...
btnYleiskatsaus.setOnClickListener(onMenuClikkedListener);
...
}
}
private OnClickListener onMenuClikkedListener = new OnClickListener() {
@Override
public void onClick(View v) {
...
}
};
}
布局文件布局sw720dp陆/ activity_navigation.xml
看起来这
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/pressed_koti"
android:orientation="vertical" >
<ListView
android:id="@+id/valikko"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" >
</ListView>
</LinearLayout>
下面是 activity_koti.xml
文件。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<fragment
android:id="@+id/menuFragment"
android:layout_width="300dp"
android:layout_height="match_parent"
class="fi.peltoset.mikko.home.Navigation" />
<fragment
android:id="@+id/contentFragment"
android:layout_width="fill_parent"
android:layout_height="match_parent" />
</LinearLayout>
我跑了Android 4.1.2模拟器的应用程序。
I ran the application on an emulator with Android 4.1.2.
是什么原因导致这些错误,我如何解决这些问题?
What causes these errors and how do I fix them?
推荐答案
您应该使用安卓名称
来指向您的片段,而不是类
,还必须包含相同属性的第二个片段,这可以解释名== NULL
。
You should use android:name
to point to your fragments instead of class
, it is also necessary to include the same attribute for your second fragment, this would explain the name==null
.
修改 <一个href="http://stackoverflow.com/questions/10162983/activity-layout-fragment-class-vs-androidname-attributes">Apparently类可以互换与Android:名称,但我会按照文档使用什么
Apparently class may be interchangeable with android:name, but I would follow what the docs use.
这应该是;
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<fragment
android:id="@+id/menuFragment"
android:layout_width="300dp"
android:layout_height="match_parent"
android:name="fi.peltoset.mikko.home.Navigation" />
<fragment
android:id="@+id/contentFragment"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:name="I NEED A NAME" />
</LinearLayout>
<一个href="http://developer.android.com/training/basics/fragments/creating.html#AddInLayout">http://developer.android.com/training/basics/fragments/creating.html#AddInLayout
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